Sydney school evacuated after gas leak

About 750 students and teachers at a high school in Sydney's southwest were forced to evacuate due to a gas leak, emergency services say.

They were called to Ingleburn High School just after 9.30am on Tuesday after the leak was detected in the science lab.

"A bunsen burner tap was left on," a Fire & Rescue spokesman said.

All 750 students and teachers were sent to the school's oval while the leak was checked.

Fifteen students and three teachers were examined by paramedics after becoming unwell due to the effects of the gas, but none needed to be taken to hospital.

The gas leak was later contained and the students and teachers returned to class.